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In microbiology, the colony-forming unit (CFU) assay stands as the gold standard for assessing the viability of cells. It is a simple and reliable method that offers a way to enumerate viable cells across various contexts, from food safety to drug discovery. However, despite its efficiency, the CFU assay has its drawbacks, notably its time- and resource-intensive nature and the generation of substantial plastic waste.
Over the years, scientists have sought alternatives to enhance the scalability and efficiency of viability measurements. Strategies have ranged from robotic liquid handling and imaging to microfluidics and viability stains. While these methods are a successful alternative, none have quite matched the simplicity, versatility, and low cost of the traditional CFU assay—until now.
The Geometric Viability Assay (GVA) is a novel approach that uses geometry to accurately quantify viable cells in a sample, with the ability to measure a remarkable dynamic range, from 1 to 1,000,000 viable cells by simply using a single pipette tip per sample. By filling the pipette tip with colonies suspended in agarose gel and analysing their axial distribution, GVA uses geometric principles to calculate the total number of viable cells in the sample. The probability of colony formation varies along the length of the cone, with colonies nearer the base more likely to form than those nearer the tip, due to differences in the cross-sectional area.
The researchers behind GVA have demonstrated its precision and accuracy in quantifying viability across a wide range of cell concentrations. One of the most attractive features of GVA is its simplicity and efficiency. By using a universal tool in microbiology—the pipette tip—GVA minimizes consumables and reduces operator time by over 30-fold compared to the CFU assay. This streamlined approach not only enhances throughput but also mitigates environmental impact by reducing plastic waste—a pressing concern in modern laboratory practices.
While the approach is still in its early stages, it has great potential to be the method of choice for high-throughput viability screening across diverse applications, from research to industrial settings. With the ability to reduce time and reagents required while maintaining the quantitative and versality of the CFU standard that have made it the established method for viability counts in microbiology – what are you waiting for … try it?
Reference
Meyer, C.T., Lynch, G.K., Stamo, D.F. et al. A high-throughput and low-waste viability assay for microbes. Nat Microbiol 8, 2304–2314 (2023). https://doi.org/10.1038/s41564-023-01513-9